05 November 2004
What is corticobasal degeneration?
Corticobasal degeneration (CBD) is a rare neurological disease in which parts of
the brain deteriorate or degenerate. CBD is also known as corticobasal
ganglionic degeneration, or CBGD.
Several regions of the brain degenerate in CBD. The cortex, or outer layer of
the brain, is severely affected, especially the fronto-parietal regions, located
near the center-top of the head. Other, deeper brain regions are also affected,
including parts of the basal ganglia, hence the name "corticobasal"
degeneration. The combined loss of brain tissue in all these areas causes the
symptoms and findings seen in people with CBD.
What causes the degeneration of brain tissue in CBD?
Unfortunately, the cause of CBD is entirely unknown. There is currently no
strong evidence to suggest CBD is an inherited disease, and no other risk
factors, such as toxins or infections, have been identified.
Studies of brain tissue of individuals with CBD show certain characteristic
cell changes. Similar, although not identical, changes are observed in two other
neurodegenerative diseases, Pick's disease and progressive supranuclear palsy.
These changes, involving a brain protein called tau, have provided researchers
some initial clues in their search for the causes of CBD.
What are the symptoms of CBD?
Symptoms of CBD usually begin after age 60. The initial symptoms of CBD are
often stiffness, shakiness, jerkiness, slowness, and clumsiness, in either the
upper or lower extremities. Other initial symptoms may include dysphasia
(difficulty with speech generation), dysarthria (difficulty with articulation),
difficulty controlling the muscles of the face and mouth, or walking and balance
difficulties. Symptoms usually begin on one side of the body, and spread
gradually to the other. Some patients (probably more than commonly recognized in
the past) may have memory or behavioral problems as the earliest or presenting
CBD is a progressive disease, meaning the symptoms worsen over time. Over the
course of one to several years, most people with CBD gradually worsen, with
symptoms progressing to involve upper and lower extremities and other body
regions. Symptoms of advanced CBD include:
- parkinsonism (rigidity, slow movements, postural instability)
- myoclonus (sudden, brief jerky movements)
- dystonia, including blepharospasm
- speech difficulty
- mild-to-moderate cognitive impairment (memory loss, difficulty planning or
executing unrehearsed movements, dementia)
- sensory loss
- "alien hand/limb" phenomenon (difficulty controlling the
movements of a limb, which seems to undertake movements on its own,
sometimes combined with a feeling that the limb is not one's own)
How is CBD diagnosed?
Early in the disease course, it is often difficult to distinguish CBD from
similar neurodegenerative diseases. Diagnosis of CBD involves a careful
neurological exam, combined with one or more types of laboratory evaluations.
Electrophysiological studies, including an EEG (electroencephalogram), may show
changes in brain function over time that are consistent with the
neurodegeneration. CT or MRI scans can also be used in this way, providing
images of asymmetric atrophy of the fronto-parietal regions of the brain's
cortex, the regions most frequently involved in the disease.
How is CBD treated?
Unfortunately, there are no drugs or other therapies that can slow the progress
of the disease, and very few that offer symptomatic relief. Tremor and myoclonus
may be controlled somewhat with drugs such as clonazepam. Baclofen may help
reduce rigidity somewhat. Levodopa and other dopaminergic drugs used in
Parkinson's disease are rarely beneficial, but may help some CBD patients.
Physical therapy exercises may be useful to maintain range of motion of stiff
joints. This may prevent pain and contracture (muscle shortening), and help
maintain mobility. Occupational therapy may be used to design adaptive equipment
that supports the activities of daily living, thus helping to maintain more
functional independence. Speech therapy is used to improve articulation and
What is the usual course of CBD?
A person with CBD will usually become immobile due to rigidity within five years
of symptom onset, and may require a gastrostomy tube for feeding at some point
before that. Most often, within ten years of onset, pneumonia or other bacterial
infections may lead to life-threatening complications.